Liquid adhesive, such as hot melt adhesive, is applied onto various components during manufacture of disposable absorbent personal hygiene products such as diapers, adult incontinence products, and feminine hygiene products. Dispensing systems have been developed for applying hot melt adhesive onto various components of the disposable absorbent personal hygiene product. In one example, these dispensing systems apply one or more hot melt adhesive filaments to a nonwoven substrate, which is then adhered to one or more thin elastic strands to form an elasticized portion of the disposable absorbent personal hygiene product. Downstream of the dispensing system, the various components (e.g., flat substrate layers and elastic strands) pass through a pressure nip to secure the components together.
Many disposable absorbent personal hygiene products include elasticized leg gathers adjacent to leg openings to secure the personal hygiene product against the user's legs and contain any waste material captured by the personal hygiene product. In these applications, a high level of creep resistance is desirable. “Creep” of an elastic strand is defined as the movement of either end of the elastic strand from an initial location where the end is adhered to a substrate. If an elastic strand undergoes any significant amount of creep after assembly, at least one end of the elastic strand will effectively de-bond from the substrate and reduce the ability of the elasticized portion to remain firmly engaged with the skin surface. To avoid this undesirable creep, a high quality bond must be formed by the adhesive applied to the elastic strand so that the elastic strand does not de-bond from the substrate.
One well understood method of improving the quality of an adhesive bond and thereby reducing creep is by applying additional adhesive on the substrate or the elastic strands. However, applying too much adhesive to an elastic strand locks the elastic strand along its length and thereby reduces the effectiveness of the elastic material to apply force to the substrate. In other words, the elastic strand loses the ability to apply sufficient retraction force to the substrate. Moreover, increasing the amount of adhesive used in disposable absorbent personal hygiene product manufacturing significantly increases cost and also reduces the “hand” or softness of the resulting product. Applying too much adhesive material may also lead to “burn through,” which occurs when the adhesive material burns or melts through the adhered substrate. Consequently, the amount of adhesive used to adhere elastic strands to substrates should be minimized while also maintaining a high level of creep resistance, a high retraction force, and minimized burn through and stiffness.
Elasticized leg gathers are formed along opposing side edges of the personal hygiene product. The side edges are generally curved to follow the contour of a leg. It is therefore desirable to apply the one or more elastic strands along a curvilinear path adjacent to the side edges, which improves the fit of the elasticized portion around the legs of a user. To this end, applying non-linear or curved elastic strands to a substrate of the personal hygiene product enables a more comfortable fit and better leakage protection compared to straight elastic strands that do not closely follow the contour of the side edges.
Conventional systems for applying a curved elastic strand to a substrate of a personal hygiene product generally include an oscillating strand roller or guide that must be positioned in close proximity to the substrate so that the stretched elastic strand(s) are applied accurately and under sufficient tension along a desired non-linear path. When multiple elastic strands are applied in each leg gather, the limited clearance between the oscillating strand guide and the substrate also prevents the multiple elastic strands from becoming tangled with one another prior to application to the substrate. The limited clearance is generally on the order of one centimeter, which does not provide enough space for a dispensing module or nozzle to apply adhesive to the elastic strands. Moreover, the high amount of oscillatory movement that would be required for a dispensing module or nozzle to follow the elastic strands in the limited clearance downstream of the oscillating strand guides could apply unacceptably high levels of “g-force” to the dispensing module or nozzle, depending on specific application parameters.
As a result, conventional systems for applying curved elastic strands to a substrate generally apply adhesive along the desired non-linear path on the substrate prior to application of the elastic strand(s) to the substrate. To ensure that the elastic strand(s) are sufficiently adhered to the substrate, an excessively large amount of adhesive must be applied to the desired non-linear path. However, the application of a large amount of adhesive is undesirable for many of the reasons described above, including but not limited to reduced softness or hand, limited force retraction, and increased cost.
There is a need, therefore, for an adhesive dispensing system and method that addresses one or more of these difficulties and reduces the amount of adhesive used to form leg gathers having non-linear elastic strands.